There have been used communication apparatuses having multiple cards (including printed circuit boards) mounted in a shelf thereof. In such a communication apparatus, each card typically has thereon a central processing unit (CPU) and a random access memory (RAM), as well as a programmable logic device (PLD) which allows rewriting of circuit data on board. The PLD includes a configuration memory holding the circuit data. Rewriting the circuit data in the configuration memory updates the PLD. The circuit data is typically rewritten using a writing tool connected to an external apparatus through a cable. For this reason, if the communication apparatus is disposed in a field, such as a client site, the PLD is difficult to update.
For this reason, there have been developed communication apparatuses in recent years which have thereon cards which allow rewriting of the circuit data even in a field through software processing by a processor, such as the CPU. In such a card, the PLD typically plays an indispensable role in the operation of the processor. Accordingly, if the PLD stops other operations when it starts rewriting the circuit data, the processor may stop reading data from the RAM. Consequently, there arises a concern that the card and communication apparatus may not function normally.
As a method for reducing the concern, there have been known cards including a PLD which holds, in a configuration memory thereof, circuit data to be rewritten (hereafter referred to as “a PLD to be updated”) and additionally including a device configured to output, to the PLD, a signal for rewriting the circuit data (hereafter referred to as “a device used for update”; this signal will be referred to as a configuration signal). In such a card, a CPU transfers circuit data in the RAM to the device used for update through software processing and stores the data therein. Next, with the PLD to be updated, the CPU, and the RAM stopped in the card, the device used for update autonomously rewrites the circuit data held in the configuration memory of the PLD to be updated on the basis of the configuration signal. Thus, the PLD is updated.
Japanese Laid-open Patent Publication No. 9-218781 is an example of related art.